Towards an understanding of the oxidation state of cobalt and manganese ions in framework substituted microporous aluminophosphate redox catalysts: An electron paramagnetic resonance and X-ray absorption spectroscopy investigation

Abstract

The local structure of manganese and cobalt ions in both the AlPO-5 and AlPO-18 materials was determined using electron paramagnetic resonance (EPR) and X-ray absorption spectroscopy (XAS). This study strongly suggested that both cobalt and manganese ions are present in the framework tetrahedral sites in the as-prepared materials. Upon calcination, in a dry atmosphere, both manganese and cobalt ions are partially oxidised to the 3+ state; the fraction of oxidised cobalt or manganese ions depends upon both the nature of the framework structure and on the ion type with manganese systems showing a higher proportion of oxidised cations.